1. Field of the Invention
This invention relates to a oscillation circuit suitable for high-frequency oscillation, and particularly to a high-frequency oscillation circuit having a feedback loop which can be used for a high frequency circuit of communication equipment and the like to improve a frequency and amplitude characteristics of the oscillation signals.
2. Description of the Prior Art
In general, a high-frequency circuit used for a communication equipment such as TV, radio receiver, high-frequency radio equipment, and a high-frequency measuring instrument and the like move a signal from the base band to the high-frequency band and vice verse.
For this, the high-frequency circuit mixes signals in the base band or high frequency signals with carrier signals originating from a local oscillation source. This local oscillation source comprises colpitts oscillator, Hartley oscillator, clap oscillator, or other oscillators modified from the above.
However, since the oscillators in the conventional art generate harmonic components in the oscillation signal, an additional band pass filter or band stop amplifier in the oscillators is necessary to reduce the harmonic components. In addition, since the oscillators in the conventional art include numerous harmonic components in the oscillation signal, a filter circuit has to be included in the oscillator in order to reduce the spurious and it is difficult to design a broadband pass amplifier. Further, the harmonic components in the oscillating signals give considerable burden to the receiving circuit, since which cause problems of image signals in the receiving circuit. Furthermore, there are many problems, such as the increase of loss of signals, circuit complexity, and manufacturing cost.
A conventional high-frequency oscillation circuit is shown in FIG. 1. Referring to FIG. 1, the high-frequency oscillation circuit are composed of a resonance circuit part 10 and an oscillation circuit part 20, and the resonance circuit part 10 and the oscillation circuit part 20 are connected each other by a coupling capacitor 16. The resonance part 10 is composed of an inductor 12 and a capacitor 14. The oscillation circuit part 20 includes a bipolar transistor 22, a resistor 24 and a capacitor 26 connected in parallel between the emitter and ground of the bipolar transistor 22, and a capacitor 28 connected between the emitter and the base of the bipolar transistor 22. A power source 30 is connected to the base and collector of the bipolar transistor 22 through the resistors 32 and 34 which are connected in parallel.
Wherein, the capacitor 16 is placed between the resonance circuit part 10 and the oscillation circuit part 20 and passes alternating signals only. The bipolar transistor 22 is driven by the voltage which is applied through the resistor 32 from the voltage source 30. The resistor 32 is a bias resistor of the bipolar transistor 22 and regulates the voltage value supplied to the base of the bipolar transistor 22. The resistor 34 functions as a load resistor of the bipolar transistor 22.
The resistor 24 of the oscillation circuit part 20 is connected to the emitter of the bipolar transistor 22 and limits the quantity of the current flowing on the emitter of the bipolar transistor 22. The capacitor 26 bypasses the high-frequency noise signal and matches the impedances of the base and the emitter of the bipolar transistor 22. The capacitor 28 feed back the signal originating from the emitter of the bipolar transistor 22 into the base thereof. The capacitors 26 and 28 set up the phase condition of the oscillation circuit.
In the conventional high-frequency oscillation circuit having such a construction, the oscillation frequency is determined by the unique resonance frequency of the resonance circuit part 10, the capacitances of the capacitors 26 and 28, and the inner capacitance value of the bipolar transistor 22.
However, the capacitors 26 and 28 used in the conventional oscillation circuit have a problem that the gain of the feedback loop 20 cannot be enlarged because of the restriction on the composition due to the of phase condition of the oscillation circuit. Accordingly, the oscillation circuit of the conventional art has to use a transistor having high cutoff frequency, and the resulting oscillation signal includes numerous harmonic components. Therefore, the oscillation circuit of the conventional art has the problem that band pass filter, band stop amplifier and the like have to be added thereto.
Therefore, an object of the present invention is to provide a high-frequency oscillation circuit in which harmonic components of a oscillation signal can be reduced.
Another object of the present invention is to provide a high-frequency oscillation circuit capable of enhancing the frequency characteristics of the oscillating signals.
Another object of the present invention is to provide a high-frequency oscillation circuit in which manufacturing cost can be reduced.
Another object of the present invention is to manufacture a high-frequency oscillation circuit as a monolithic circuit with ease.
Another object of the present invention is to construct an oscillator in which C/N ratio and the oscillation level are high simultaneously.
To achieve the objects of the present invention, a high-frequency oscillation circuit having a feedback loop according to the present invention comprises: resonance means for generating oscillation frequency signals; amplifying means having an input port for receiving the signals originating from the resonance means and for amplifying the signals originating from the resonance means; an inductive element having one port connected to the output port of the amplifying means; and a capacitive element having one port connected to the other port of the inductive element; wherein the connection point of the inductive element and the capacitive element is connected to the input port of the amplifying means.
Also, to achieve the objects of the present invention, a high-frequency oscillation circuit according to the present invention comprises: resonance means for generating oscillation frequency signals; amplifying means having an input port for receiving the signals originating from the resonance means and for amplifying the signals originating from the resonance means; a T-shaped matching element having one port connected to the output port of the amplifying means; and a capacitive element having one port connected to the other port of the T-shaped matching element; wherein the other port of the capacitive element is grounded, wherein the connection point of the T-shaped matching element and the capacitive element is connected to the input port of the amplifying means.
Also, to achieve the objects of the present invention, in a high-frequency oscillation circuit according to the present invention, the inductive element or the T-shaped matching element forms a part of the feedback loop which feeds back the output signal originating from the output port of the amplifying means into the input terminal, and the inductive element or T-shaped matching element and capacitor compose an impedance matching means for matching the impedances of both ports of the feedback loop, and the gain of the oscillation signal is maximized, and the impedance matching means forms the resonance circuit and the low pass filter.
Also, to achieve the objects of the present invention, a high-frequency oscillation circuit according to the present invention comprises: resonance means for generating oscillation frequency signals; amplifying means having an input port for receiving the signals originating from the resonance means and for amplifying the signals originating from the resonance means; a strip line having one port connected to the output port of the amplifying means; and a capacitive element having one port connected to said one port of the strip line, wherein the other port of the capacitive element is grounded, wherein the other port of the strip line is connected to the input port of the amplifying means.
Now, preferred embodiments of the high-frequency oscillation circuit in accordance with the present invention will be described with reference to accompanying drawings.
The present invention will not be limited to the embodiments described below, and many modifications can be performed within the same field of the technology.